Engine systems may utilize recirculation of exhaust gas from an engine exhaust system to an engine intake system, a process referred to as exhaust gas recirculation (EGR), to reduce regulated emissions. For example, a turbocharged engine system may include a low-pressure (LP) EGR system which recirculates exhaust gas from the exhaust system to the intake passage upstream of a turbocharger compressor. An intake oxygen sensor may be located in the engine intake downstream from the compressor to provide an indication of EGR flow.
The inventors herein have recognized various issues with the above system. In particular, intake oxygen sensor (IAO2) measurements for determining exhaust gas recirculation (EGR) in low pressure EGR vehicle systems can be corrupted when purging fuel vapors to a boosted intake side of an engine. The purge fuel vapors can react on the surface of the oxygen sensor element and reduce the oxygen sensor element sensitivity. Accordingly, changes in oxygen concentration at the engine intake measured by the oxygen sensor are smaller than actual changes in oxygen concentration. The reduced change in oxygen concentration is interpreted by the engine control system as an erroneous larger than actual EGR. Engine operation with low EGR can lead to high engine temperatures, reduced fuel economy, increased NOx emissions, among other disadvantages.
To address the above issues, the inventors herein have identified that one example approach comprises measuring the oxygen concentration at the engine intake during a first condition when the EGR is off, boost pressure and manifold pressures are greater than the barometric pressure, and the canister purge is on. In this way, a purge fuel concentration can be estimated from the measured oxygen concentration. Furthermore, a purge correction factor can be determined from the estimated purge fuel concentration. During a second condition when the EGR is on, boost pressure and manifold pressures are greater than the barometric pressure, and the canister purge is on, the measured oxygen concentration can be corrected using the purge correction factor in order to determine the proper EGR. In this way, it is possible to compensate for possible corruption in EGR control caused by vapor purging, while still enabling the purging to continue.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.